25
To erase the imaging screens, place the imaging screen against the front panel of the
Eraser-K with the white phosphor side facing the white diffuser plate of the unit. Set the
timer to the desired setting or to erase continuously set the timer to the HOLD position.
The erasure process typically requires only 10 minutes, assuming the previous sample has
not charged the phosphor in the screen above 20,000 pixel density units. An erasing time
guideline is shown in Table 4.3.
Note: The screen will not be damaged by extended erasure.
Note: Erasing the screen to the basal level is critical, since this has a direct effect on the
sensitivity, linear response, quantitation, exposure time and image quality.
Erasure Guidelines
Table 4.3. Recommended erasure times.
4.4.3 How to Prepare Samples
The recommended phosphor screen exposure time can be estimated, based on one-tenth
of the time it would normally take to visualize the sample on x-ray film.
Dry Radioactive Samples
Dry thin samples such as nitrocellulose membranes, dried gels or TLC sheets can be
exposed directly to the imaging screen in the exposure cassette (Figure 4.10). Ensure that
TLC plates are completely dry before placing them against the screen and always cover
with plastic wrap to prevent flecks from contaminating the screen.
When imaging thick samples it is recommended that the screen is simply placed face down
against the sample on a flat surface and the exposure is conducted in a light-tight drawer
or other dark location.
Note: It is important when placing the screen against the sample, that the samples are
correctly aligned the first time. Adjusting the screen after placement against the sample
may result in a ghost image or double exposure. If the screen needs to be realigned it must
first be erased.
Note: If you are exposing the screen to a frozen sample, the screen should first be sealed
in a plastic bag as condensation may cause screen damage. After exposure the screen
should be equilibrated to room temperature before the bag is opened and the screen
removed.
Caution: Never expose screens to organic solvents or acetic acid vapors as these may
cause screen damage even when the sample is covered with plastic wrap.
Caution: Samples should not contain either scintillants or enhancers, as these will interfere
with the operation of the screen.
Condition
Background
(PD units)
Time
Before each exposure
1-20,000
10 minutes
After high dosage
exposure
>20,000
20
minutes
!
